| Developing ColdFusion MX Applications with CFML |
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Using Query of Queries |
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| Developing ColdFusion MX Applications with CFML |
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Using Query of Queries |
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The following sections discuss Query of Queries functionality. If you know SQL or have interacted with databases, you might be familiar with some of these features.
ColdFusion supports using dot notation in table names.
If a structure named A contains a field named B, which contains a table named Products, you can refer to the table with dot notation, as follows:
SELECT tape_ID, length
FROM A.B.Products;
A join operation uses a single SELECT statement to return a result set from multiple tables. The re are two main types of JOIN operations:
ColdFusion does not support OUTER JOINs, nor does it support the INNER JOIN syntax, as the following example shows:
SELECT Dog_ID, Breed_ID,
FROM Dogs INNER JOIN Breed ON Dogs.Dog_ID = Breed.Dog_ID;
ColdFusion supports INNER JOINs between two tables, as the following example shows. This operation is the most common type of join.
SELECT Dog_ID, Breed_ID
FROM Dogs, Breed WHERE Dogs.Dog_ID = Breed.Dog_ID;
The UNION operator lets you combine the results of two or more SELECT expressions into a single record set. The original tables must have the same number of columns, and corresponding columns must be UNION-compatible data types. Columns are UNION-compatible data types if they meet one of the following conditions:
Note: Query Of Queries does not support ODBC-formatted dates and times.
select_expression = select_expression UNION [ALL] select_expression
This example uses the following tables:
| Table1 |
|
|---|---|
| Type(int) |
Name(varchar) |
| 1 |
Tennis |
| 2 |
Baseball |
| 3 |
Football |
| Table2 |
|
|---|---|
| ID(int) |
Sport(varchar) |
| 3 |
Football |
| 4 |
Volleyball |
| 5 |
PingPong |
To combine Table1 and Table2, use a UNION statement, as follows:
SELECT * FROM Table1
UNION SELECT * FROM Table2
The UNION statement produces the following result (UNION) table:
| Result table |
|
|---|---|
| Type(int) |
Name(varchar) |
| 1 |
Tennis |
| 2 |
Baseball |
| 3 |
Football |
| 4 |
Volleyball |
| 5 |
PingPong |
The column names of a UNION table are the column names in the result set of the first SELECT statement in the UNION operation; ColdFusion ignores the column names in the other SELECT statement. To change the column names of the result table, you can use an alias, as follows:
Select Type as SportType, Name as SportName from Table1
UNION Select * from Table2
By default, the UNION operator removes duplicate rows from the result table. If you use the keyword ALL, then duplicates are included.
You can combine an unlimited number of tables using the UNION operator, for example:
Select * from Table1
UNION Select * from Table2 UNION Select * from Table3 ...
By default, the Query of Queries SQL engine evaluates a statement containing UNION operators from left to right. You can use parentheses to change the order of evaluation. For example, the following two statements are different:
/* First statement. */
SELECT * FROM TableA UNION ALL (SELECT * FROM TableB UNION SELECT * FROM TableC ) /* Second statement. */ (SELECT * FROM TableA UNION ALL SELECT * FROM TableB ) UNION SELECT * FROM TableC
In the first statement, there are no duplicates in the union between TableB and TableC. Then, in the union between that set and TableA, the ALL keyword includes the duplicates. In the second statement, duplicates are included in the union between TableA and TableB but are eliminated in the subsequent union with TableC. The ALL keyword has no effect on the final result of this expression.
When you perform a UNION, the individual SELECT statements cannot have their own ORDER BY or COMPUTE clauses. You can only have one ORDER BY or COMPUTE clause after the last SELECT statement; this clause is applied to the final, combined result set. You can only specify GROUP BY and HAVING expressions in the individual SELECT statements.
ColdFusion lets you use the following conditional operators in your SQL statements:
This conditional tests whether a Boolean expression is true, false, or unknown.
SELECT _isValid FROM Chemicals
WHERE _isValid IS true;
This conditional tests whether an expression is null.
null_cond ::= expression IS [NOT] NULL
SELECT bloodVal FROM Standards
WHERE bloodVal IS NOT null;
This conditional lets you compare an expression against another expression of the same data type (Numeric, String, Date, or Boolean). You can use it to selectively retrieve only the relevant rows of a record set.
comparison_cond ::= expression [> | >= | <> | != | < | <=] expression
The following example uses a comparison conditional to retrieve only those dogs whose IQ is at least 150:
SELECT dog_name, dog_IQ
FROM Dogs WHERE dog_IQ >= 150;
This conditional lets you compare an expression against another expression. You can use it to selectively retrieve only the relevant rows of a record set. Like the comparison conditional, the BETWEEN conditional makes a comparison; however, the between conditional makes a comparison against a range of values. Therefore, its syntax requires two values, which are inclusive, a minimum and a maximum. You must separate these values with the AND keyword.
between_cond ::= expression [NOT] BETWEEN expression AND expression
The following example uses a BETWEEN conditional to retrieve only those dogs whose IQ is between 150 and 165, inclusive:
SELECT dog_name, dog_IQ
FROM Dogs WHERE dog_IQ BETWEEN 150 AND 165;
This conditional lets you specify a comma-delimited list of conditions to match. It is similar in function to the OR conditional. In addition to being more legible when working with long lists, the IN conditional can contain another SELECT statement.
in_cond ::= expression [NOT] IN (expression_list)
The following example uses the IN conditional to retrieve only those dogs who were born at either Ken's Kennels or Barb's Breeders:
SELECT dog_name, dog_IQ, Kennel_ID
FROM Dogs
WHERE kennel_ID IN ('Kens','Barbs');
This conditional lets you perform wildcard searches, in which you compare your data to search patterns. This strategy differs from other conditionals, such as BETWEEN or IN, because the LIKE conditional compares your data to a value that is partially unknown.
like_cond ::= left_string_exp [NOT] LIKE right_string_exp [ESCAPE escape_char]
The left_string_exp can be either a constant string, or a column reference to a string column. The right_string_exp can be either a column reference to a string column, or a search pattern. A search pattern is a search condition that consists of literal text and at least one wildcard character. A wildcard character is a special character that represents an unknown part of a search pattern, and is interpreted as follows:
Note: Earlier versions of ColdFusion do not support bracketed ranges.
The following example uses the LIKE conditional to retrieve only those dogs of the breed Terrier, whether the dog is a Boston Terrier, Jack Russell Terrier, Scottish Terrier, and so on:
SELECT dog_name, dog_IQ, breed
FROM Dogs WHERE breed LIKE '%Terrier';
The following examples are select statements that use bracketed ranges:
SELECT lname FROM Suspects WHERE lname LIKE 'A[^c]%';
SELECT lname FROM Suspects WHERE lname LIKE '[a-m]%'; SELECT lname FROM Suspects WHERE lname LIKE '%[]'; SELECT lname FROM Suspects WHERE lname LIKE 'A[%]%'; SELECT lname FROM Suspects WHERE lname LIKE 'A[^c-f]%';
ColdFusion supports two string functions, UPPER() and LOWER(), which you can use to achieve case-insensitive matching.
The following example matches only 'Sylvester':
SELECT dog_name
FROM Dogs WHERE dog_name LIKE 'Sylvester';
The following example is not case-sensitive; it uses the LOWER() function to match 'Sylvester', 'sylvester', 'SYLVESTER', and so on:
SELECT dog_name
FROM Dogs WHERE LOWER(dog_name) LIKE 'Sylvester';
You can specify your own escape character using the conditional ESCAPE clause.
The following example uses the ESCAPE clause to enable a search for a literal percent sign (%), which ColdFusion normally interprets as a wildcard character:
SELECT emp_discount
FROM Benefits WHERE emp_discount LIKE '10\%' ESCAPE '\';
Aggregate functions operate on a set of data and return a single value. Use these functions for retrieving summary information from a table, as opposed to retrieving an entire table and then operating on the record set of the entire table.
Consider using aggregate functions to perform the following operations:
Since not every relational database management system (RDBMS) supports all aggregate functions, refer to your database's documentation. The following table lists the aggregate functions that ColdFusion supports:
Note: For more information, see CFML Reference.
aggregate_func ::= <COUNT>(* | column_name) | AVG | SUM | MIN | MAX)
([ALL | DISTINCT] numeric_exp)
The following example uses the AVG() function to retrieve the average IQ of all terriers:
SELECT dog_name, AVG(dog_IQ) AS avg_IQ
FROM Dogs WHERE breed LIKE '%Terrier';
ColdFusion supports aggregate functions of any arbitrary expression, as follows:
SELECT lorange, count(lorange+hirange)
FROM roysched GROUP BY lorange;
ColdFusion supports mathematical expressions that include aggregate functions, as follows:
SELECT MIN(lorange) + MAX(hirange)
FROM roysched GROUP BY lorange;
ColdFusion supports the use of any arbitrary arithmetic expression, as long as it is referenced by an alias.
The following code is correct:
SELECT (lorange + hirange)/2 AS midrange,
COUNT(*) FROM roysched GROUP BY midrange;
The following code is correct:
SELECT (lorange+hirange)/2 AS x,
COUNT(*) FROM roysched GROUP BY x HAVING x > 10000;
The following code is not supported in Query of Queries:
SELECT (lorange + hirange)/2 AS midrange,
COUNT(*) FROM roysched GROUP BY (lorange + hirange)/2;
ColdFusion supports the ORDER BY clause to sort. Make sure that it is the last clause in your SELECT statement. You can sort by multiple columns, by relative column position, by nonselected columns. You can specify a descending sort direction with the DESC keyword (by default, most RDBMS sorts are ascending, which makes the ASC keyword unnecessary).
order_by_column ::= ( <IDENTIFIER> | <INTEGER_LITERAL> ) [<ASC> | <DESC>]
The following example shows a simple sort using an ORDER BY clause:
SELECT acetylcholine_levels, dopamine_levels
FROM results ORDER BY dopamine_levels
The following example shows a more complex sort; results are first sorted by ascending levels of dopamine, then by descending levels of acetylcholine. The ASC keyword is unnecessary, and is used only for legibility.
SELECT acetylcholine_levels, dopamine_levels
FROM results ORDER BY 2 ASC, 1 DESC
ColdFusion supports the use of database column aliases. An alias is an alternate name for a database field or value. ColdFusion lets you reuse an alias in the same SQL statement.
One way to create an alias is to concatenate (append) two or more columns to generate a value. For example, you can concatenate a first name and a last name to create the value fullname. Because the new value does not exist in a database, you refer to it by its alias. The AS keyword assigns the alias in the SELECT statement.
ColdFusion supports alias substitutions in the ORDER BY, GROUP BY, and HAVING clauses.
Note: ColdFusion does not support aliases for table names.
SELECT FirstName + ' ' + LastName AS fullname
from Employee;
The following examples rely on these two master queries:
<cfquery name="employee" datasource="2pubs">
SELECT * FROM employee </cfquery> <cfquery name="roysched" datasource="2pubs"> SELECT * FROM roysched </cfquery>
To generate output for the following examples, use the cfdump tag. For example, use <cfdump var="#order_by#"> for the following ORDER BY example.
<cfquery name="order_by" dbtype="query">
SELECT (job_id + job_lvl)/2 AS job_value FROM employee ORDER BY job_value </cfquery>
<cfquery name="group_by" dbtype="query">
SELECT lorange+hirange AS x, count(hirange) FROM roysched GROUP BY x </cfquery>
<cfquery name="having" dbtype="query">
SELECT (lorange+hirange)/2 AS x, COUNT(*) FROM roysched GROUP BY x HAVING x > 10000 </cfquery>
ColdFusion uses Boolean logic to handle conditional expressions. Proper handling of NULL values requires the use of ternary logic. The IS [NOT] NULL clause works correctly in ColdFusion. However the following expressions do not work properly when the column breed is NULL:
WHERE (breed > 'A')
WHERE NOT (breed > 'A')
The correct behavior should not include NULL breed columns in the result set of either expression. To avoid this limitation, you can add an explicit rule to the conditionals and rewrite them in the following forms:
WHERE breed IS NOT NULL AND (breed > 'A')
WHERE breed IS NOT NULL AND not (breed > 'A')
ColdFusion has a list of reserved keywords, which are typically part of the SQL language and are not normally used for names of columns or tables. To escape a reserved keyword for a column name or table name, enclose it in brackets.
Caution: Earlier versions of ColdFusion let you use some reserved keywords without escaping them.
ColdFusion supports the following SELECT statement examples:
SELECT [from] FROM parts;
SELECT [group].firstname FROM [group]; SELECT [group].[from] FROM [group];
ColdFusion does not support nested escapes, such as in the following example:
SELECT [[from]] FROM T;
The following table lists ColdFusion reserved keywords:
ABSOLUTE |
ACTION |
ADD |
ALL |
ALLOCATE |
ALTER |
AND |
ANY |
ARE |
AS |
ASC |
ASSERTION |
AT |
AUTHORIZATION |
AVG |
BEGIN |
BETWEEN |
BIT |
BIT_LENGTH |
BOTH |
BY |
CASCADE |
CASCADED |
CASE |
CAST |
CATALOG |
CHAR |
CHARACTER |
CHARACTER_LENGTH |
CHAR_LENGTH |
CHECK |
CLOSE |
COALESCE |
COLLATE |
COLLATION |
COLUMN |
COMMIT |
CONNECT |
CONNECTION |
CONSTRAINT |
CONSTRAINTS |
CONTINUE |
CONVERT |
CORRESPONDING |
COUNT |
CREATE |
CROSS |
CURRENT |
CURRENT_DATE |
CURRENT_TIME |
CURRENT_TIMESTAMP |
CURRENT_USER |
CURSOR |
DATE |
DAY |
DEALLOCATE |
DEC |
DECIMAL |
DECLARE |
DEFAULT |
DEFERRABLE |
DEFERRED |
DELETE |
DESC |
DESCRIBE |
DESCRIPTOR |
DIAGNOSTICS |
DISCONNECT |
DISTINCT |
DOMAIN |
DOUBLE |
DROP |
ELSE |
END |
END-EXEC |
ESCAPE |
EXCEPT |
EXCEPTION |
EXEC |
EXECUTE |
EXISTS |
EXTERNAL |
EXTRACT |
FALSE |
FETCH |
FIRST |
FLOAT |
FOR |
FOREIGN |
FOUND |
FROM |
FULL |
GET |
GLOBAL |
GO |
GOTO |
GRANT |
GROUP |
HAVING |
HOUR |
IDENTITY |
IMMEDIATE |
IN |
INDICATOR |
INITIALLY |
INNER |
INPUT |
INSENSITIVE |
INSERT |
INT |
INTEGER |
INTERSECT |
INTERVAL |
INTO |
IS |
ISOLATION |
JOIN |
KEY |
LANGUAGE |
LAST |
LEADING |
LEFT |
LEVEL |
LIKE |
LOCAL |
LOWER |
MATCH |
MAX |
MIN |
MINUTE |
MODULE |
MONTH |
NAMES |
NATIONAL |
NATURAL |
NCHAR |
NEXT |
NO |
NOT |
NULL |
NULLIF |
NUMERIC |
OCTET_LENGTH |
OF |
ON |
ONLY |
OPEN |
OPTION |
OR |
ORDER |
OUTER |
OUTPUT |
OVERLAPS |
PAD |
PARTIAL |
POSITION |
PRECISION |
PREPARE |
PRESERVE |
PRIMARY |
PRIOR |
PRIVILEGES |
PROCEDURE |
PUBLIC |
READ |
REAL |
REFERENCES |
RELATIVE |
RESTRICT |
REVOKE |
RIGHT |
ROLLBACK |
ROWS |
SCHEMA |
SCROLL |
SECOND |
SECTION |
SELECT |
SESSION |
SESSION_USER |
SET |
SIZE |
SMALLINT |
SOME |
SPACE |
SQL |
SQLCODE |
SQLERROR |
SQLSTATE |
SUBSTRING |
SUM |
SYSTEM_USER |
TABLE |
TEMPORARY |
THEN |
TIME |
TIMESTAMP |
TIMEZONE_HOUR |
TIMEZONE_MINUTE |
TO |
TRAILING |
TRANSACTION |
TRANSLATE |
TRANSLATION |
TRIM |
TRUE |
UNION |
UNIQUE |
UNKNOWN |
UPDATE |
UPPER |
USAGE |
USER |
USING |
VALUE |
VALUES |
VARCHAR |
VARYING |
VIEW |
WHEN |
WHENEVER |
WHERE |
WITH |
WORK |
WRITE |
YEAR |
ZONE |